With the aid of MR microscopy, the mustached bat, pteronotus parnellii, has been shown to have normal enlargements (hydrops) in certain regions of the cohlea (scala media). These enlargements occur in specific areas related to very sharp tuning. It is important to determine if this is a morphological feature common to all cochleas in regions of greatest sensitivity. It is also important to determine if this is related primarily to high frequencies and to address the question as to whether there are morphologcial differences among animals specialized for high vs. low frequency hearing. The purpose of this research is to obtain high resolution images which will allow us to reconstruct the scalae in several species of small mammals. To do this we propose to use two rodents (gerbils, guinea pigs) whose frequency sensitivity and hearing capacitites are well documented. In addition to pteronotus, we will use the bat Eptesicus fuscus whose hearing capacities are very different from those of the moustached bat.